Metallocenes constitute useful catalysts for olefin polymerization when combined with a cocatalyst such as an aluminoxane. It is generally accepted that the properties of the polymers formed using such catalyst combinations are determined in large part by the structural nature of the metallocene, including the steric and electronic features imparted to the complex by its cyclopentadienyl ligands. Therefore, there is a continuing need to develop improved methods for preparing metallocenes and their precursor ligands that allow for a range of diverse substituents to be incorporated into the ligand structure. There is also a need for improved methods for preparing metallocenes that provide the desired compounds as well as their precursor ligands in higher yield and/or greater purity.
One step in the preparation of certain metallocenes is the isolation of an intermediate fulvene. Fulvenes have the general formula C4R″4C═CRR′ and the following structure:
wherein R, R′, and R″ are generally and independently hydrocarbyl or hydrogen. As precursors to cyclopentadienyl ligands and metallocene compounds, fulvenes can provide a means for integrating a range of substituents into the metallocene structure. One aspect of this utility can be seen from the reaction of fulvenes with anionic cyclopentadienyl (Cp), indenyl (Ind), or fluorenyl (Flu) reagents as illustrated in Scheme 1, because the resulting products can be used as ligand precursors to form bridged or ansa-metallocenes. Ansa-metallocene catalysts are useful in olefin polymerizations in part because of the impact the tailored ligand set can have on the properties of the resulting polymer.

Therefore, it is of interest to develop new methods to prepare fulvenes that may provide these ligands in higher yields, greater selectively, and/or greater purity. It is also of interest to develop new methods to prepare ansa-metallocenes based on new fulvene synthetic methods.